1. Field of the Invention
This invention generally relates to fuel supply control for gas turbines. More particularly, this invention relates to a fuel supply for gas turbines having a plurality of solenoid valves that are controlled to achieve a desired fuel flow rate.
2. Description of the Prior Art
Gas turbines are well known and used in various applications. Common elements within all gas turbines include a compressed air source, a fuel supply, a fuel combustor and a power turbine. The fuel and compressed air are mixed within the combustor where they are ignited and the resulting energy powers the turbine. There are a variety of configurations and variations upon the basic turbine structure.
In many situations, the fuel supply includes a primary portion and a secondary portion. A flow divider valve is often incorporated into the system to control the flow of fuel to the primary or secondary portions of the fuel supply. For example, the flow divider valve is controlled to direct fuel flow to the primary fuel supply portion during engine start-up while fuel is directed through the secondary portion during normal engine operation. While flow divider valves have proven effective for this purpose, they tend to introduce complexity and expense into the system. Accordingly, it is desirable to provide an alternative to conventional flow divider valve arrangements.
While other types of valves are commercially available, there are control considerations that must be accommodated to effectively and properly operate most gas turbines. The requirements for controlling the timing of fuel flow into the combustor cannot be accommodated by most simple valves. For example, an electrically driven solenoid valve, which presents an economically attractive arrangement, typically does not have adequate response time to provide desired fuel flow control. Given the operating frequencies and the need to tightly control the amount of fuel flow for most turbines, a typical solenoid valve will not provide adequate performance. The possibility exists for the solenoid to remain closed for too long, which presents the possibility for engine flameout. On the other hand, attempting to pulse larger amounts of fuel flow at a relatively low frequency, which may be within the solenoid operating range, tends to cause large releases of energy from the turbine which is typically accompanied by undesirable additional noise.
There is a need for an improved valving arrangement to control fuel flow in a gas turbine that is capable of operating at frequency levels where the amount of fuel is tightly controlled so that the desired turbine operation is achieved without additional noise.
This invention addresses that need while eliminating the requirement for a flow divider valve.
In general terms, this invention is a fuel flow control system for use in a gas turbine.
A system designed according to this invention includes a fuel source. At least one manifold is coupled with the fuel source. A plurality of nozzles near an end of the manifold allow fuel to exit the manifold. A plurality of solenoid valves are associated with the manifold between the nozzles and the fuel source. A controller selectively opens and closes the solenoid valves, respectively, to provide a desired amount of fuel flow through the nozzles.
The controller preferably uses pulse width modulation in one example to control the solenoid valves and a time within a cycle during which fuel flows through the nozzles is greater than an open time for any one of the solenoid valves. The open times for the solenoid valves are set and timed relative to each other (i.e., phase controlled) so that the total fuel flow is as desired.
In one example, the manifold includes a primary portion and a secondary portion. At least one solenoid valve is associated with the primary portion. At least one solenoid valve is associated with the secondary portion. It is preferred to include more than one solenoid valve associated with the secondary portion. The controller preferably utilizes the solenoid valve associated with the primary portion to allow fuel flow through the primary portion during engine start up, for example. The controller controls operation of the solenoids associated with the secondary portion to provide fuel flow during normal engine operation.
In one example, each solenoid is associated with selected nozzles so that controlling the operation of each solenoid controls fuel flow through specific nozzles of the manifold assembly.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.